Japanese Unexamined Patent Application Publication No. H5-305585 by the present applicant (Patent Document 1) discloses a technology of the compliance control of both legs of a two-legged mobile robot. This technology is applicable also to a robot having, for example, four legs.
In this case, according to the compliance control based on the technology disclosed in the publication, a virtual plane is inclined while all legs are in contact with the virtual plane, so that an undulation or tilt over a large area of the floor can be coped with. According to the technology of the publication, however, there have been cases where a load (floor reaction force) is not properly distributed if a floor has a local tilt, projection or depression. As a result, poor contact with a surface has sometimes occurred, causing a portion (foot) to be in contact therewith to shake or to be subjected to an undue landing impact, with consequent deteriorated properties of foot contact with the ground. This has further led to a danger in that a robot easily slips or spins. Further, there have been cases where control fails to properly distribute a floor reaction force moment for restoring the posture of the robot to a desired posture to the distal portion of each leg, causing the posture of the robot to shake. There have been also cases where, if a certain portion of the robot starts vibrating, then it is inconveniently difficult to attenuate the vibration.
Further, there have been cases where the failure of proper control of distribution of a floor reaction force to the distal end of each leg results in excessive load on some actuators.
In addition, Japanese Unexamined Patent Application Publication No. H10-277969 (Patent Document 2) and Japanese Unexamined Patent Application Publication No. 2001-322076 (Patent Document 3) by the present applicant disclose a technology for composite-compliance control and a technology for estimating the configuration of a floor.
These technologies make it possible to properly distribute a floor reaction force to the distal portion of each leg in a two-legged mobile robot and to compositively estimate the configuration of a floor, more specifically, compositively and accurately estimate the inclination of the ground contact surface of each leg distal portion and the height difference between ground contact surfaces at the same time. These technologies in the publications are, in principle, applicable to a multi-legged robot, such as a four-legged robot; however, no description has been given of a technology for specifically applying them.
Further, there has been known a technique for estimating the height of a floor at the time of landing by using feelers (load sensors or contact sensors) provided at the distal ends of the legs of the four-legged robot.
However, this technique is a sequential technique and has been incapable of dealing with a case where a floor deforms after landing, as with a soft ground. Especially when the main body of the robot is severely vibrating, such as when the robot is moving fast, the height of a floor cannot be correctly estimated, and there has been a danger in that load is not properly distributed to each leg.
There has been also known a technology whereby the compliance control of each leg of a robot is independently conducted for each leg. This technology, however, does not take into account the fact that the legs interfere with each other through the vibration of the body of the robot. In other words, the compliance control is individually carried out on each leg. For this reason, the compliance control of each leg does not act in harmony, making it impossible to properly distribute a floor reaction force to each leg.
The present invention has been made with a view of the background described above, and it is an object thereof to provide a device that is resistant to the influences of an unknown slope, projection or depression of a floor with which a mobile body, such as a legged mobile robot or a wheeled mobile body having an active suspension, comes in contact, and that properly controls a floor reaction force. Moreover, an object of the present invention is to provide a device capable of properly controlling a floor reaction force while accurately estimating the configuration of a floor.